The complex and hierarchical underwater world of the Algeans is gradually revealed and explained through the eyes of various members of its community, starting with the young Lyko, who knows very little. We learn from those at various levels within the strict hierarchy how the community functions and how it came into being, ending with the savior, who had a vision and set out to save the human race. As Lyko discovers more about her world, she comes to realise that she has an important connection with the savior which will have dangerous consequences for herself and her friend, Sebastian.
The Algean world is on a constant state of alert for attack from an enemy; unknown to anybody but the savior. Will their fears be realised and, if so, will the community be able to unite against an unknown enemy and ensure the survival of the next generation?